PHASE-EQUILIBRIA OF THE GA-NI-AS TERNARY-SYSTEM

Phase equilibria were investigated in the Ga-Ni-As ternary system, wit h particular emphasis on the regions of technological importance to Ni /GaAs electrical contacts. A 600 degrees C Gibbs isotherm was construc ted using x-ray-diffraction analysis and electron probe microanalysis of annealed samples. Additionally, three isopleths (NiAs-GaAs, NiGa-Ni As, and NiGa-GaAs) and a partial liquidus projection were established using differential thermal analysis and metallography. These data were utilized to clarify some discrepancies in the literature pertaining t o the constitution of the Ga-Ni-As system, particularly questions abou t the existence of ternary phases. It was demonstrated that at 600 deg rees C, previously reported ternary phases were actually specific comp ositions of the binary phase, NiAs, which exhibits significant ternary solubility. Additional x-ray-diffraction and differential thermal ana lysis experiments suggested that superlattice structures based on the NiAs structure may become stable at lower temperatures. A ternary eute ctic reaction was shown to occur at 810+/-5 degrees C, with eutectic p oint at the composition Ni(0.48)Ga(0.30)AS(0.22). The existence of thi s eutectic reaction has important ramifications for the development of Ni-based electrical contacts to GaAs because any metallization scheme with a composition within the region bounded by NiGa, NiAs, and GaAs, as well as elemental Ni, will experience at least partial liquid form ation at temperatures greater than 810 degrees C. (C) 1996 American In stitute of Physics.